U.S. patent application number 13/255930 was filed with the patent office on 2012-03-22 for novel composite materials comprising a thermoplastic matrix polymer and wood particles.
This patent application is currently assigned to ONBONE OY. Invention is credited to Antti Parssinen.
Application Number | 20120071590 13/255930 |
Document ID | / |
Family ID | 40510249 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120071590 |
Kind Code |
A1 |
Parssinen; Antti |
March 22, 2012 |
Novel composite materials comprising a thermoplastic matrix polymer
and wood particles
Abstract
The present invention concerns a novel low-temperature
thermoplastic wood-biopolymer composite comprised of small wood
particles and a polycaprolactone (PCL) homopolymer for use in
medical procedures including orthopedic casting or splinting. The
material is made from a thermoplastic composite that softens when
heated to approximately 60.degree. C., after which it can be formed
directly on the patient. The composite then retains its shape as it
cools down. The material is composed of epsilon caprolactone
homopolymer reinforced with discontinuous short length wood
particles.
Inventors: |
Parssinen; Antti; (Helsinki,
FI) |
Assignee: |
ONBONE OY
Helsinki
FI
|
Family ID: |
40510249 |
Appl. No.: |
13/255930 |
Filed: |
March 11, 2010 |
PCT Filed: |
March 11, 2010 |
PCT NO: |
PCT/FI10/50185 |
371 Date: |
November 30, 2011 |
Current U.S.
Class: |
524/13 |
Current CPC
Class: |
A61F 5/058 20130101;
Y10T 428/249921 20150401; A43B 17/003 20130101; C08L 97/02
20130101; A61L 15/125 20130101; A61L 15/12 20130101; C08L 2201/06
20130101; C08L 67/04 20130101; A61F 5/14 20130101; A63B 2209/00
20130101; A63B 2071/1258 20130101; A61L 15/14 20130101; C08L
2203/02 20130101; A61L 15/12 20130101; C08L 67/04 20130101 |
Class at
Publication: |
524/13 |
International
Class: |
C08L 97/02 20060101
C08L097/02; C08L 67/04 20060101 C08L067/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2009 |
FI |
20095251 |
Claims
1. A composite material, comprising a first component formed by a
polymer and a second component formed by a reinforcing material,
wherein the first component comprises a thermoplastic polymer
selected from the group of biodegradable polymers and mixtures
thereof, and the second component comprises a woody material of
platy wood particles having a smallest dimension greater than 0.1
mm.
2. The composite material according to claim 1, wherein the woody
material derived from the platy wood particles forms at least 10%
of the total weight of the second component.
3. The composite material according to claim 1, comprising: 5 to 99
parts by weight of a thermoplastic polymer component, and 1 to 95
parts by weight of a woody material, the weight of the woody
material being calculated based on the dry weight of said wood
material.
4. The composite material according to claim 1, wherein the first
component forms the matrix of the composite, and the microstructure
of the second components is discontinuous.
5. The composite material according to claim 1, wherein the
thermoplastic polymer is selected from the group of
epsilon-caprolactone homopolymers, blends of epsilon-caprolactone
homopolymers and other biodegradable thermoplastic homopolymers,
with 5-99 wt % of an epsilon-caprolactone homopolymer and 1-95 wt %
of a biodegrable thermoplastic polymer, and copolymers of
epsilon-caprolactone homopolymer and any thermoplastic biodegrable
polymer, with 5 to 99 wt % of repeating units derived from
epsilon-caprolactone and 1 to 95 wt % repeating units derived from
other polymerizable material.
6. The composite material according to claim 1, comprising a first
polymer component having an average molecular weight of
approximately 60,000 to 500,000 g/mol.
7. The composite material according to claim 1, comprising a first
polymer component having an inherent viscosity in excess of 1
dl/g.
8. The composite material according to claim 1, wherein the density
of the composition is at least 5% less than that of the
epsilon-caprolactone homopolymer.
9. The composite material according to claim 1, wherein the 3-point
bending force of the composition is at least 5% better than that of
the epsilon-caprolactone homopolymer as such.
10. The composite material according to claim 1, wherein the
Young's modulus values in 3-bending test of the composition is at
least 10% higher than that of the epsilon-caprolactone
homopolymer.
11. The composite material according to claim 1, wherein the platy
wood particles have an average size (of the smallest dimension) of
at least 0.5 mm.
12. The composite material according to claim 1, wherein the
individual wood particles have at least two dimensions greater than
1 mm and one greater than 0.1, said wood particles having an
average volume of at least 1 mm.sup.3.
13. The composite material according to claim 1, wherein the wood
particles are such that it is possible visually see six surfaces of
the particles.
14. The composite according to claim 1, wherein the wood particles
are capable of being orientated and aligned in a melt flow of the
thermoplastic polymer.
15. The composite according to claim 1, wherein the wood particles
comprise chips of hardwood, softwood or a combination thereof.
16. The composite according to claim 1, further comprising a
particulate material, a fibrous material or a combination thereof
as a reinforcing component, said component forming approximately 1
to 15% of the weight of the second component.
17. (canceled)
18. The composite material according to claim 1 arranged in the
form of a finger splint, a wrist cast or an ankle cast.
19. The composite material according to claim 1, said material
being formable at a temperature of approximately 50 to 70.degree.
C. and being rigid at a temperature of less than 50.degree. C.
20. A composite material comprising a first component formed by a
polymer and a second component formed by a reinforcing material,
wherein the first component comprises a thermoplastic polymer
selected from the group of biodegradable polymers and mixtures
thereof, and the second component comprises a woody material, the
majority of the woody material being made up of wood particles
greater in size than powder.
21. The composite material according to claim 20, said majority of
wood particles greater in size than powder being granular or platy
and making up more than 70% of the woody material, said woody
material making up more than 70% of the second component.
22. The composite material according to claim 20, said woody
material comprising substantially granular particles having a cubic
shape with dimensions from greater than 0.6 mm up to approximately
3.0 mm.
23. The composite material according to claim 22, wherein the woody
material comprises or consists essentially of granular particles
having an average, sieved size of greater than 0.6 mm up to
approximately 3.0 mm.
24. The composite material according to claim 21, wherein said
first component thermoplastic polymers are in pellet form and have
dimensions similar to those of the woody material granular
particles, and wherein the mixture of first and second components
in the composite material is homogeneous.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to polymer materials, such as
reinforced polymer materials, which are useful as orthopedic
materials. In particular, the present invention concerns a
composite material comprising a first component formed by a polymer
and a second component formed by a reinforcing material. The
invention also concerns the use of the polymer materials for
casting and splinting.
[0003] 2. Description of Related Art
[0004] Casting is the most common form of external splinting and it
is used for a wide array of bone and soft-tissue injuries. In this
context, the function of the cast is to immobilize and to protect
the injury and, especially, to minimize motion across a fracture
site.
[0005] A number of casting materials are known. The first
generation of casting material is formed by plaster of paris (in
the following abbreviated "POP"). Largely owing to its low cost and
ease of molding it has gained universal acceptance. There are,
however, a number of disadvantages of POP, including long setting
times, messy application, low strength and relative heaviness.
Although setting takes only a few minutes, drying may take many
hours or days, especially if the atmosphere is moist and cool.
Impacts on the plaster while it is setting may cause a weakening of
the material. Furthermore, the transparency to X-rays (in the
following "radiolucency") is poor.
[0006] The second generation of casting materials is formed by
synthetic composite materials, such as fiberglass reinforced
polyurethane resins. They are useful alternatives to conventional
plaster of paris and are gaining increasing popularity. Fiberglass
and resinous materials can safely be applied as external splints.
These materials are lightweight, durable and waterproof but require
protective packaging and they are difficult to apply. Further on,
some of the fiberglass casting materials during applying requires
special gloves for avoiding penetration of small fiberglass
particles through skin. In addition, synthetic casting materials
may have a shorter setting and solidification time than traditional
plaster-based materials. Further, they are much more expensive than
plaster at present, but to balance this disadvantage, fewer
bandages are required and they are much more durable in everyday
use. They are also more radiolucent than plaster based casting
materials.
[0007] In cases of fracture a splint, rather than a cast, may be
applied in the emergency room. Principally, a splint can be made of
the above materials, including plaster and fiberglass, but also
from aluminum and moldable plastics. Such a splint is usually
wrapped with an elastic bandage and the rigid portion does not
envelope the limb circumferentially. It allows for some expansion
of the dressing if significant swelling is anticipated.
Nonetheless, elevation is just as critical. After an appropriate
amount of time, a splint may be replaced by a cast. Both
traditional casts and aluminium sheet or foil backed casts must be
kept dry during the application and before setting is complete.
[0008] Finger splints used for broken or dislocated digits or in
tendon injuries are usually made of alumafoam (an aluminium strip
padded on one side with sponge-like foam). Sometimes plaster can
also be used either alone or in combination with alumafoam.
[0009] Casting materials containing fibres or powder of natural
substances are known in the art. WO 2007/035875 discloses a
cross-linked thermoplastic material with aramide fibres wherein
some wood pulp or natural fibres has been incorporated. In WO
94/03211 a composite of saw dust and polycaprolactone is discussed,
US Patent Application No. 2008/0103423 concerns a combination of
cork and polycaprolactone. The material exhibits some degree of
flexibility which allows for some freedom at movements and swelling
of the limb.
[0010] None of the above discussed materials combine properties of
mechanical rigidity, reusability, easy molding and inexpensive
price. A further problem is the difficulty to correct the form of
the cast after hardening. For the present-day materials, the cast
has to be broken up and replaced by a new, if it turns out that the
fracture site has been improperly immobilized. The aluminium sheets
and foils used in the above-mentioned casts are difficult to
recycle and form non-biodegrable medical waste.
SUMMARY OF THE INVENTION
[0011] It is an aim of the present invention to eliminate at least
a part of the disadvantages of the prior art and to provide a novel
material for immobilization of fracture sites in hard- and
soft-tissues, in particular in mammals, such as humans.
[0012] The present invention is based on the idea of producing a
biodegradable orthopedic material having thermoplastic properties.
The material is obtained by combining a first polymer component
formed by a thermoplastic polymer and a second reinforcing
component formed by particles of a biodegradable natural material.
The thermoplastic polymer forms the matrix of the material and said
particles a discontinuous phase within the matrix.
[0013] In particular, the particles comprise finely divided
particles of wood or of a similar raw-material, having a granular
and in particular generally platy structure. Such particles can be
wood chips or a similar raw-material having a granular structure or
a generally platy structure. The particles can be capable of being
orientated for example within a laminar flow or uniaxial extension
of the thermoplastic polymer. The thermoplastic polymer is a
biodegradable material (typically a material capable of being
broken down especially into innocuous products by the action of
living thing and in the presence of water and/or oxygen). Examples
of polymers suitable for the present purpose are lactic acid
polymer, polylactide, polyglycolide and, in particular,
caprolactone homo- or copolymers, the polymer material being
selected such that the composite softens when it is heated to a
temperature of approximately 50 to 70.degree. C., after which it
can be formed directly on the patient.
[0014] In another embodiment, the composite material comprises a
second component formed by a woody material, the majority of which
is being made up of wood particles greater in size than powder.
[0015] Thus, the present material can be used as a casting or
splinting material.
[0016] More specifically, the material according to the present
invention is mainly characterized by what is stated in the
characterizing parts of claims 1 and 19.
[0017] Considerable advantages are obtained by the present
invention.
[0018] Thus, the splinting material of the present invention can be
used in a similar fashion as the known materials. Importantly, in
these applications it eliminates many, if not all, of the
disadvantages of conventional materials, such as plaster of Paris
and synthetic fiberglass reinforced materials.
[0019] In a preferred embodiment, the novel wood-plastic composite
(WPC) is in toto biodegradable. The material is composed of epsilon
caprolactone homopolymer or copolymer or a blend of thermoplastic,
biodegradable polymers, optionally combined with conventional
thermoplastic materials, and reinforced with discontinuous short
length particles of wood or of a similar material, optionally
complemented with fibrous materials.
[0020] The wood particles orientate in the polymer matrix and
provide a self-reinforcement effect. As a result, the present
material has good dimensional stability and shaped into a sheet
which cannot be easily punctuated under point loading.
[0021] The biodegrable thermoplastic material in the composite can
be a caprolactone homopolymer, copolymer of different monomers e.g.
caprolactone, lactide and/or glycolide or a blend of different
homopolymers, e.g. polycaprolactone, polylactide and polyglycolide
homopolymers.
[0022] The preferred polymer component comprises polycaprolactone
which is a biologically acceptable material; some grades even
having an FDA approval for internal use in humans. The other
component, the woody particles, is also non-toxic. Both of these
components are compostable and the novel composite can be used
without harm or risk to end-users or patients.
[0023] The material of the present invention is ready to be applied
for casting or splinting after a warm-up procedure and does not
require a messy multistep preparation, like traditional plasters
and fiber reinforced resins.
[0024] Heating and cooling of the composite can be repeated without
changes in the mechanical properties of the material. Therefore,
the splint may be remolded and reused on the same patient for the
whole recovery time. The total volume of the waste and pollution is
therefore diminished.
[0025] The material has waterproof and water resistant properties.
In one embodiment the material is considered waterproof as it can
be heated e.g. in water without causing damage to the material or
loosing the geometry of it. In another embodiment the material is
considered to have water resistant properties in that it can be
cleaned under running water without causing damage to the material
or losing its geometry. In either case, the material is considered
spill-proof.
[0026] In particular, the material of the present invention is
moldable at temperatures comfortable against skin and after cooling
to the temperature of surroundings it is substantially rigid and
slightly flexible so that it comfortably retains its geometry.
[0027] When the material is heated close to its melting point, it
is possible to attach to it various fastening means (e.g. Velcro)
to appliances produced thereof. Naturally any other kinds of straps
and hooks and laces can be attached as well, and the surface of the
material will readily attach bandage and typical wound care gauze
film.
[0028] The temperature required for molding lies in the range of
about 60 to 70.degree. C. and the thermal conductivity of the
material is so low that in clinical use the cast or splint can
safely be applied even directly on the skin. At this temperature,
the material is soli and pliable and the created form closely
matches the anatomical contours of the patient's body or body
part.
[0029] The splinting material tolerates strong twisting and it can
be bent even to relatively sharp, or acute, angles without causing
fractures or wrinkles. The wrinkles of splints cause soft tissue
damages during long healing process of the fracture and are
therefore undesirable.
[0030] The splinting material of the present invention is produced
from radiolucent components. This is advantageous in fracture
fixation applications because the removal of the splint or cast can
be avoided when using X-ray imaging.
[0031] The material can also be used in manufacturing of orthoses
e.g. foot-supporting devices or insoles and sport orthoses devices
e.g. shin pad, in which their shock-absorbing properties are
particularly useful. They can be plastically deformed and the
reinforcement distributes compression and impact forces over a
large area. In sport appliances, such as grips for rackets in
rackets sports, as well as in the above-mentioned foot-supporting
applications, the capability of the material easily to be formed
such that it takes up the impression formed by the hand or foot are
quite useful. The material can also be used in consumer goods,
three-dimensional artwork e.g. jewellery and sculptures, products
requiring biodegrading e.g. vessels for plantation.
[0032] Next the invention will be examined more closely with the
aid of a detailed description and referring to the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] In the drawings,
[0034] FIG. 1 is a bar chart showing the stress force of test
sample in 3-point bending test of wood-PCL composites;
[0035] FIG. 2 is a graphical representation of the specific modulus
(E/.rho.) of test sample in 3-point bending test;
[0036] FIG. 3 shows the densities of composites having different
sized wood particles.
[0037] FIG. 4 shows in a schematic side-view the use of the present
material as a cast for treating ruptures of the extensor tendon in
a the first finger joint;
[0038] FIG. 5 shows a schematic fashion a front-view of a
reshapable wrist cast;
[0039] FIG. 6 shows in a schematic fashion a front-view of an
anatomic ankle cast according to an embodiment of the invention;
and
[0040] FIG. 7a shows the front and side views of an unfolded
anatomic ankle cast of the kind depicted in FIG. 6, and FIG. 7b
shows the side view of the same cast in folded position.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0041] As evident from the above, the material of the present
invention can be simply manufactured by mixing the first component,
i.e. a suitable polymer material for example in the form of
pellets, with the second component i.e. wood particles or granules,
by melt mixing. The mixing can be carried out in any conventional
apparatus designated for melt mixing or melt processing. One
example is a heatable vessel having a mechanical stirrer.
[0042] The uniformity of the composite can be increased by using an
extruder, kneader or any device suitable for mixing thermoplastic
polymers.
[0043] By using an extruder mixing apparatus, two hoppers, each
containing one of the components of the material, can deposited the
desired amount of each component in to the mixing chamber of the
apparatus. Then, by way of the mixing means in the mixing
apparatus, there is formed a homogeneous mixture of the first and
second components prior to the formation of the formation of the
material.
[0044] One advantage to the material being formed by such a
homogeneous mixture of the components is that the forces necessary
to form a substantially homogeneous material are reduced.
Therefore, little or no compression three is necessary to
facilitate mixing of the components in a material formation step.
The importance of this factor is that, by way of the homogeneous
mixture, larger particles of each component can be used which would
otherwise have been destroyed when subjected to high compression
forces.
[0045] The material can be applied for use after it has been
recovered from the mixing device and formed into desired shape for
example into a sheet or plate or roll or any similar planar,
folded, bent or tubular structure, but the material can even be
formed directly on the patient.
[0046] The material mixed with an extruder can be shaped with
appropriate nozzle to the shape of e.g. rectangular sheet or plate
which can be used directly after cutting e.g. as a finger
splint.
[0047] The desired profile for the splints can be manufactured with
the extruder manufactured sheet or plate with e.g. laser cutting,
water jet cutting, eccentric pressing or with any tool capable for
producing regular shape profiles. The present material can also be
process with compression moulding, injection moulding, die-casting,
and pressure die-casting.
[0048] The sheet or plate can have a thickness of, generally about
1 to 50 mm, in particular about 1.5 to 30 mm, for example 1.5 to 20
mm. A typical thickness is about 2 to 6 mm. The length and the
width of the sheet or plate can vary in the range of about 1 to 150
cm (length) and 1 to 50 cm (width), a typical length being about 10
to 60 cm and a typical width being about 5 to 20 cm.
[0049] The proportions between the components of the material can
vary in a broad range. Thus, generally, 5 to 99 wt-%, for example
40 to 99 wt-%, of the material is formed by the thermoplastic
polymer component and 1 to 95 wt-%, for example 1 to 60 wt-%, by
the woody material.
[0050] The weight ratio of polymer-to-wood can easily be modified
and the weight percent of wood, based on the total weight/volume of
the composition, may vary between 1 and 70%, preferably however in
the range of 10 to 60 weight percent, or 20 to 60 weight percent,
and 15 to 50%, or 25 to 50% by volume.
[0051] The second component comprises or consists essentially of a
woody material having a smallest diameter of greater than 0.1 mm.
As will be discussed below, there can also be other wood particles
present in the second component. The woody material can be granular
or platy. According to one embodiment, the second component
comprises a woody material derived from platy wood particles having
a smallest diameter of greater than 0.1 mm.
[0052] Thus, generally, the wood component can be characterized
generally as being greater in size than powder.
[0053] The size and the shape of the wood particles may be regular
or irregular. Typically, the particles have an average size (of the
smallest dimension) in excess of 0.1 mm, advantageously in excess
of 0.5 mm, for example in excess of 0.6 mm, suitably about 1 to 40
mm, in particular about 1.2 to 20 mm, preferably about 1.5 to 10
mm, for example about 1.5 to 7 mm. The length of the particles
(longest dimension of the particles) can vary from a value of
greater than 1 mm to value of about 1.8 to 200 mm, for example 3 to
21 mm.
[0054] The woody particles can be granular, platy or a mixture of
both. Woody particles considered to be granular have a cubic shape
whose ratio of general dimensions are on the order of
thickness:width:length=1:1:1. In practice it is difficult to
measure each individual particle to determine if it is a perfect
cube. Therefore, in practice, particles considered to be granular
are those where one dimension is not substantially different than
the other two.
[0055] Woody particles considered to be platy means that they have
generally a plate-shaped character, although particles of other
forms are often included in the material. The ratio of the
thickness of the plate to the smaller of the width or length of the
plate's edges is generally 1:1 to 1:500, in particular about 1:2 to
1:50. Preferably, the woody particles include at least 10% by
weight of chip-like particles, in which the ratio of general
dimension are on the order of thickness:width:length=1:1-20:1-100,
with at least one of the dimension being substantially different
than another.
[0056] Based on the above, the platy particles of the present
invention generally comprise wood particles having at least two
dimensions greater than 1 mm and one greater than 0.1 mm, the
average volume of the wood particles being generally at least 0.1
mm.sup.3 more specifically at least 1 mm.sup.3.
[0057] "Derived from platy wood particles" designates that the wood
particles may have undergone some modification during the
processing of the composition. For example, if blending of the
first and second components is carried out with a mechanical melt
processor, some of the original platy wood particles may be
deformed to an extent.
[0058] The majority of wood particles greater in size than powder,
which particles may be granular or platy, typically make up more
than 70% of the woody material.
[0059] The wood species can be freely selected from deciduous and
coniferous wood species alike; beech, birch, alder, aspen, poplar,
oak, cedar, Eucalyptus, mixed tropical hardwood, pine, spruce and
larch tree for example.
[0060] Other suitable raw-materials can be used, and the woody
material of the composite can also be any manufactured wood
product.
[0061] The particles can be derived from wood raw-material
typically by cutting or chipping of the raw-material. Wood chips of
deciduous or coniferous wood species are preferred.
[0062] As mentioned above, in WO 94/03211 a composite material is
described, based upon polycaprolactone, ground almond shell and
wood flour. The known material is impaired by several
disadvantages, such as a high density of 1.1 kg/m.sup.3 or even
more, as a result of the small particle sizes of the filler
material [wood, less than 600 microns (600 .mu.m)]. Another
disadvantage related to the use of small particle sized fillers, is
the poor adhesive properties of composite material. According to
our experiments (cf. Example 10 below), composites consisting of 40
weight percentage of wood dust sized between 0-800 microns reveal
zero adhesion toward bandage material (compression force of 0.1
bars).
[0063] To avoid mobilization of the splint and to improve
immobilization of the fractured limb during setting of the bandages
minor adhesion threes are required, Further on, polycaprolactone
polymer (CARA 656) presented in examples of WO 94/03211 has too low
viscosity (melt flow index value of 7 g/10 minutes with 2.16 kg
standard die at 160.degree. C.) to be used at practical applying
temperature of 65.degree. C. The composite manufactured of PCL
having MET value of seven (PCL-7) tears too easily and does not
tolerate strong bending during applying.
[0064] By contrast, the present composite materials provide
excellent properties also in this respect.
[0065] In addition to wood chips and other platy particles, the
present composition can contain reinforcing fibrous material, for
example cellulose fibers, such as flax or seed fibers of cotton,
wood skin, leaf or bark fibers of jute, hemp, soybean, banana or
coconut, stalk fibers (straws) of hey, rice, barley and other crops
and plants including plants having hollow stem which belong to main
class of Tracheobionta and e.g. the subclass of meadow grasses
(bamboo, reed, scouring rush, wild angelica and grass).
[0066] Furthermore, the composition may contain particulate or
powdered material, such as sawdust, typically having particles with
a size of less than 0.5 mm*0.5 mm*0.5 mm. Particulate or powdered
material is characterised typically as material of a size in which
the naked eye can no longer distinguish unique sides of the
particle. Platy particles are easily recognizable as one dimension
is recognizable by the naked eye as being larger than another.
Granular particles, While having substantially equal dimensions,
are of such dimension that their unique sides can be determined by
the naked eye and, oriented.
[0067] More particularly, particulate or powdered materials are of
such a small or fine size that they cannot he easily oriented, with
respect to their neighbours. Granular and platy particles are of
such as size that their sides are recognizable and
orientatable.
[0068] The desired composition of the second component can be
achieved by sifting woody particles through one or more meshes
having one or more varying qualities. The desired composition can
also be accomplished by other well known techniques in the art for
sorting and separating particles in to desired categories. The
desired composition may he the resultant composition of one sifting
or separating process. The desired composition may also be a
mixture of resultant compositions from several sifting or
separation processes.
[0069] A particularly interesting raw-material comprises wood
particles, chips or granules, of any of the above mentioned wood
species having a screened size of greater than 0.6 mm up to about
3.0 mm, in particular about 1 to 2.5 mm on an average.
[0070] According to one embodiment, the weight ratio of fibrous
material (optionally including said powdered material) to the platy
material (dry weight) is about 1:100 to 100:1, preferably about
5:100 to 50:50. In particular, the woody material derived, from the
platy wood particles forms at least 10%, preferably about 20 to
100%, in particular about 30 to 100%, of the total weight of the
second component.
[0071] The woody material makes up at least and preferably more
than 70% of the second component.
[0072] In addition to wood-based powdered materials, inorganic
particulates or powdered materials such as mica, silica, silica
gel, calcium carbonate and other calcium salts such as tricalcium
orthophosphate, carbon, clays and kaolin may be present or
added.
[0073] According to an alternative, a composite useful as an
orthopedic material, comprises a first component formed by a
polymer and a second component formed by a reinforcing material,
wherein the first component comprises a thermoplastic polymer
selected from the group of biodegradable polymers and mixtures
thereof, and the second component comprises reinforcing fibres.
Such fibers can be selected from the group for example of cellulose
fibers, such as flax or seed fibers of cotton, wood skin, leaf or
bark fibers of jute, hemp, soybean, banana or coconut, stalk fibers
(straws) of hey, rice, barley and other crops including bamboo and
grass. According to an interesting embodiment, the wood filler may
consist of or consist essentially of fibres of the indicated kind.
The polymer component can be any of the below listed polymers,
caprolactone homo- or copolymers having a molecular weight of about
60,000 g/mol or 65,000 g/mol up to 250,000 g/mol being particularly
preferred.
[0074] The thermoplastic polymer and its properties will be
discussed in more detail below, but for the sake of order it is
pointed out that in all of the above mentioned embodiments, Wherein
various fillers are used as a second and a third and even fourth
component of the composition, substantial advantages with respect
to biodegradability and mechanical properties have been found using
caprolactone polymers, in particular homopolymers, as
thermoplastics. The particularly preferred polymer component is a
caprolactone homopolymers having a molecular weight of above 80,000
g/mol. Specifically, caprolactone having a molecular weight of
between 100,000 g/mol and 200,000 g/mol as been found to be
advantageous both in terms of resultant properties and cost.
[0075] Before the woody particles are mixed with the thermoplastic
polymer they can be surface treated, e.g. sized, with agents, which
modify their properties of hydrophobicity/hydrophobicity and
surface tension. Such agents may introduce functional groups on the
surface of the granules to provide for covalent bonding to the
matrix. Even increased hydrogen bonding or bonding due to van der
Waals forces is of interest. The woody particles can also be
surface treated with polymer e.g. PCL having low viscosity and
molar mass values to increase holding powers between wood and PCL
having high viscosity value.
[0076] The wood material can be also coated or treated with
anti-rot compound e.g. vegetable oil to improve its properties
against aging and impurities.
[0077] The wood material can be dehydrated to make it lighter
before mixing it with polymer. The mechanical and chemical
properties of wood material can be improved with heat treatment,
which is known to decrease e.g. swelling and shrinkage.
[0078] In the composition according to an aspect of the present
invention, the first component the polymer) forms the matrix of the
composite, whereas the microstructure of the second component in
the composition in discontinuous. The particles of the second
component can have random orientation or they can be arranged in a
desired orientation. The desired orientation may be a predetermined
orientation.
[0079] As mentioned above, according to a preferred embodiment, a
polycaprolactone polymer n the following also abbreviated "PCL") is
used as a thermoplastic polymer in the first component of the
composition. The polycaprolactone polymer is formed by repeating
units derived from epsilon caprolactone monomers. The polymer may
be a copolymer containing repeating units derived from other
monomers, such as lactic acid, glycolic acid, but preferably the
polymer contains at least 80% by volume of epsilon caprolactone
monomers, in particular at least 90% by volume and in particular
about 95 to 100% epsilon caprolactone monomers.
[0080] In a preferred embodiment, the thermoplastic polymer is
selected from the group of epsilon-caprolactone homopolymers,
blends of epsilon-caprolactone homopolymers and other biodegradable
thermoplastic homopolymers, with 5-99 wt %, in particular 40 to 99
wt %, of an epsilon-caprolactone homopolymer and 1-95 wt %, in
particular 1 to 60 wt %, of a biodegrable thermoplastic polymer,
and copolymers or block-copolymers of epsilon-caprolactone
homopolymer and any thermoplastic biodegrable polymer, with 5 to 99
wt %, in particular 40 to 99 wt % of repeating units derived from
epsilon-caprolactone and 1 to 95 wt %, in particular 1 to 60 wt %,
repeating units derived from other polymerizable material.
[0081] Examples of other biodegradable thermoplastic polymers
include polylactides, poly(lactic acid), polyglycotides as well as
copolymers of lactic acid and glycolic acid.
[0082] The first polymer component, in particular the epsilon
caprolactone homo- or copolymer, has an average molecular weight of
60,000 to 500,000 g/mol, for example 65,000 to 300,000/mol, in
particular at least 80,000 g/mol, preferably higher than 80,000 and
up to 250,000.
[0083] The molding properties of the present invention can be
determined by the average molecular weight (M.sub.n) of the
polymer, such as epsilon caprolactone homo- or copolymer. A
particularly preferred molecular weight range for the M.sub.n value
of PCL is from about 100,000 to about 200,000 g/mol.
[0084] The number average molar mass (Mn) and the weight average
molar mass (Mw) as well as the polydispersity (PDI) were measured
by gel permeation chromatography. Samples for GPC measurements were
taken directly from the polymerization reactor and dissolved in
tetrahydrofuran (THF). The GPC was equipped with a Waters column
set styragel HR(1,2 and 4) and a Waters 2410 Refractive Index
Detector. THF was used as eluent with a flow rate of 0.80 ml/min at
a column temperature of 35.degree. C. A conventional polystyrene
calibration was used. In determination of the water content of the
monomer at different temperatures a Metroohm 756 KF Coulometer was
used.
[0085] The properties of moldability of the present composition can
also be determined by the viscosity value of the polymer, For an
epsilon caprolactone homopolymer: when the inherent viscosity
(IV)-value of PCL is less than 1 dl/g the composite is sticky,
flows while formed and forms undesired wrinkles while cooling. When
PCL having IV-value closer to 2 dl/g is used the composite
maintains its geometry during molding on the patient and it may be
handled without adhesive properties. Thus, IV values in excess of 1
dl/g are preferred, values in excess to 1.2 dl/g are preferred and
values in excess of 1.3 dl/g are particularly suitable.
Advantageously the values are in the range of about 1.5 to 2.5
dl/g, for example 1.6 to 2.1 dl/g. Inherent Viscosity values were
determined by LAUDA PVS 2.55d rheometer at 25.degree. C. The
samples were prepared by solvating 1 mg of PCL in 1 ml chloroform
(CH.sub.3Cl).
[0086] A particularly important feature of the thermoplastic
polymer is the viscosity which is relatively high, typically at
least 1,800 Pas at 70.degree. C., 1/10 s; the present examples show
that the viscosity can be on the order of 8,000 to 13,000 Pas at
70.degree. C., 1/10 s (dynamic viscosity, measured from melt
phase). Below the indicated value, a reinforced material readily
wrinkles during forming it on a patient.
[0087] The thermoplastic material is preferably a biodegradable
polymer (only) but also non-biodegradable polymers may be utilized.
Examples of such polymers include polyolefins, e.g. polyethylene,
polypropylene, and polyesters, e.g. poly(ethylene terephthalate)
and poly(butylenes terephthalate) and polyamides. Combinations of
the above biodegradable polymers and said non-biodegradable
polymers can also be used. Generally, the weight ratio of
biodegradable polymer to any non-biodegradable polymer is 100:1 to
1:100, preferably 50:50 to 100:1 and in particular 75:25 to 100:1.
Preferably, the composite material has biodegradable properties
greater, and the material biodegrades quicker or more completely,
than the thermoplastic material alone.
[0088] According to the invention, a polymer of the afore-said kind
is preferably moldable at a temperature as low as +50.degree. C.,
in particular at +65.degree. C. or slightly above, and it can be
mixed with wood particles or generally any porous material gaining
increased rigidity of the formed composite. The polymer component,
such as polycaprolactone homopolymer, defines the form of the
splinting material against the skin.
[0089] The modulus (Young's modulus), at ambient temperature, of
the polymer component is greater than 300 MPa. By compounding the
polymer with the wood component, the modulus will be improved (cf.
below), typically it is about 350 to 2000 MPa for the
composition.
[0090] The present material contains a significant portion of wood
granules having a particle size greater than the micrometer range,
for example a size of about 0.75 mm to 50 mm. When the material is
shaped into a sheet, (at least most of) the wood granules become
oriented in two dimensions within forming of the thermoplastic
material into sheets.
[0091] According to a preferred embodiment, the present method of
producing a composite useful as an orthopedic material comprises
the steps of [0092] mixing together 10 to 100 parts, preferably 50
to 100 parts, by weight of a first component formed by a polymer
selected from the group of biodegradable polymers and mixtures
thereof, and [0093] 1 to 100 parts, preferably 10 to 50 parts, by
weight of a second component formed by a reinforcing material,
present in the form of platy wood particles.
[0094] The mixing can be melt mixing carried out at a temperature
sufficient for melting the thermoplastic polymer, e.g. at about 50
to 150.degree. C. Alternatively, the temperature can be in the
range of about 80 to 190.degree. C., preferably about 100 to
150.degree. C.
[0095] The molten polymer mass containing a mixture of biopolymer
and reinforcing platy or granular particles can be shaped manually
or, according to a preferred embodiment by moulding in a mould.
[0096] The molten polymer mass can be subjected to tensile forces
to achieve a desired orientation of the polymer and, in particular,
the reinforcing particles.
[0097] The manufacturing process can, on an industrial scale, be
carried out as follows:
[0098] In a first step wood chips or granules and plastic granules
are mixed to form a uniform blend before pouring into the feed
hopper of an extruder. The mixing process can be carried out also
by feeding of the virgin materials to the extruder directly by
using separate feeding hoppers.
[0099] The compounding is then carried out in, e.g., an extruder,
in particular a single screw extruder. in the compounding process
the screw extruder profile of the screw is preferably such that its
dimensions will allow relatively large wood chips to move along the
screw without crushing them. Thus, the channel width and flight
depth are selected so that the formation of excessive local
pressure increases, potentially causing crushing of the wood
particles, are avoided. The temperature of the cylinder and the
screw rotation speed are also selected such as to avoid
decomposition of wood chip structure by excessively high pressure
during extrusion. For example a suitable barrel temperature can be
in the range of about 110 to 150.degree. C. from hopper to die,
while the screw rotation speed was between 25-50 rpm. These are,
naturally, only indicative data and the exact settings will depend
on the actual apparatus used.
[0100] The compounded composite material obtained from the melt
processing/compounding step is then profiled in the tool to a
homogeneous product, e.g. a sheet or plate, for example using
suitable mechanical processing. One particularly suitable method is
calendaring. Another suitable process is by pressing.
[0101] To avoid changes in the structure of the wood material
during mechanical processing, the composite material can be
subjected to gentle folded between the processing steps. Usually,
the mechanical processing is carried out at a temperature well
above the glass transition/melting point of the polymer.
[0102] The density of composite manufactured typically lies in the
range of about 600 to 850 kg/m.sup.3, depending on the weight
percent of wood in material.
[0103] The manufacturing process is described in more detail in our
co-pending patent application titled "Method of Producing a
Composite Material", the content of which is herewith incorporated
by reference.
[0104] The composite retains its shape as it cools down. It is
substantially rigid but flexible so as to be supportive and
comfortable. Rigidity is generally achieved when a sample heated to
the above indicated softening temperature is cooled to below
50.degree. C., in particular to less than 45.degree. C., preferably
less than 40.degree. C. Typically, the composite is rigid at
ambient temperature, a suitable temperature of use is about 20 to
50.degree. C., in particular 22 to 40.degree. C.
[0105] The reinforced, material typically exhibits properties
selected from one or several of the following: [0106] a density of
the composition is at least 5% less than that of the polymer
component (e.g. epsilon-caprolactone homopolymer) as such; [0107] a
Young's modulus value in 3-bending test of the composition is at
least 10% higher than that of the polymer component (e.g.
epsilon-caprolactone homopolymer) as such; and [0108] a thermal
conductivity on the order of about 0.5W/mK, at the most.
[0109] At a manipulation temperature of 50 to 70.degree. C.,
typically about +65.degree. C. or slightly more, the splinting
material can be manipulated and manually shaped for up to 10
minutes and it is typically pliable for 3-10 minutes after the
finishing of heating depending of the size of splint. The material
hardens entirely in one hour. Operation time of the melt material
can be expanded by heating the material close to +100.degree. C.,
which is the temperature limit for the material to be handled
without protective gloves. The material can be heated to
+150.degree. C. and held there for several hours without changes in
the material properties.
[0110] To achieve rapid solidification of the material, a cooling
spray or a cooling gel or wrap can be used.
[0111] As mentioned above, and as will be discussed below in
connection with the examples, the present composition can be used
as a composite material according to any of the preceding claims
for use as an orthopedic material. Such materials are exemplified
by finger splints, wrist casts and ankle casts. Generally, the
platy particles form about 30 to 70%, preferably in excess of 40 up
to about 60%, of the total weight of the composition, for finger
splints and for ankle casts about 20 to 60%, preferably about 30 to
50% of the total weight of the composition. There is typically a
greater portion of the larger particles present in the larger casts
which will reduce the total weight of the cast without impairing
the strength properties thereof.
[0112] In particular, the composite material of the present
invention is manufactured in to either a blank or in to a desired,
specific shape or form. Ideally, the blanks and forms are two
dimensional and easily stackable. The blanks can be either
substantially larger than the intended size to be applied to the
animal or human being, herein referred to as the patient, or of
substantially similar size.
[0113] In the instance when the blank is of a large size than
desired, the blank can be cut with normal scissors or other
conventional cutting means before application. Such a lame blank is
preferable in the sense that one blank may be cut in to several
splints at various times according to the size required by each.
Therefore, it is not necessary to store many different shapes and
sizes of the material, which take up room and may be rarely
used.
[0114] Additionally, multiple splints may be cut from one blank in
such a way as to maximize the material used and not produce a large
amount of waste product.
[0115] Once the proper size and shaped piece of material is
obtained, cut or selected, the material is then heated to the
desired operating temperature by a heating means. Numerous heating
means are known in the art, but it is preferable to uniformly heat
the material to a specific desired temperature. If the temperature
is too high then there is risk of discomfort or harm to the
patient's skin. If the temperature is not high enough then the
material will not be able to properly conform to the patient's
body.
[0116] Therefore, in one embodiment, the composite materials are
provided along with a heater which is specifically tailored to the
application of the composite materials. The heater may have an
adjustable thermostat or may be preprogrammed to heat automatically
to the desired temperature. Ideally, the heater will have a heating
element capable of heating an entire blank or form of the composite
material evenly and completely. The size of the heater should be
sufficient enough to handle the size of the composite materials to
be used. The heater may be given complimentary along with
complementary or paid composite material blanks or forms to entice
people to use the system and material.
[0117] In cases where the heating element is other than one
specifically tailored to the present composite material it can be
selected from the range of known heating elements including contact
heaters, convection heaters, chemical heating and the like.
[0118] Once the composite material blank or form is heated to the
desired temperature, as discussed above, then the material can be
placed on the patient in the desired location to form the
exo-skeletal device. The advantage of the present material is that
it can be handled by hand without any protective requirement such
as gloves. Equally important is that the material can be formed
directly against the patient's skin. However, it can be
advantageous to have some material, such as gauze or other
cloth/cloth like material, directly in contact with the patient's
skin and to form the composite material over that material.
[0119] With the composite material still pliable and moldable, it
can be fit to contour the patient's body part nearly or exactly.
Additionally, if the initial placement is not desirable, the
material can be moved while still moldable to a more desirable
location. If the material has lost its desired moldability, then it
can be reheated and likewise moved to the new location. One of the
particular advantages of the present material is that it can be
heated and cooled many times without degrading its mechanical
properties.
[0120] When the composite material is located properly and molded
to the desired form, then it can be allowed to cool to a
temperature where it can be removed but maintain its shape. The
cooling may be accomplished by allowing the ambient conditions to
reduce the temperature of the material or the cooling may be aided
by spraying the material with water or another chemical to speed up
the cooling. Additionally, solid cooling means can be used to cool
the material such as a cold pack or ice place directly against the
composite material.
[0121] The use of the present material as a splint or cast process
is described in more detail in our co-pending patent application
titled "Orthopaedic Splinting System", the content of which is
herewith incorporated by reference.
[0122] The following non-limiting examples illustrate the
invention.
[0123] In all the below presented examples, the polycaprolactone
polymer used was a commercially available PCL homopolymer supplied
under the tradename CAPA 6800 by Perstorp Ltd., Sweden). The
polycaprolactone has a melt flow rate of about 3 g/10 min (measured
at 150.degree. C. and with a weight of 2.16 kg) and referred to as
"PCL-3". As mentioned above, another caprolactone homopolymer also
used had a significantly higher melt flow rate of about 7 g/10 min
(referred to as "PCL-7").
[0124] The wood material, if not otherwise indicated, was
conventional spruce chips produced at a Finnish saw mill. In some
of the examples wood particles of other wood species were used. The
chips, in particular the spruce chips, were occasionally used in
the form of a fraction sieved to an average size of 1-2.5 mm.
EXAMPLE 1
[0125] 78 grams of the commercially available PCL with a molecular
weight in the range of approximately 120-150 000 g/mol and 22 grams
of cubic sawmill spruce chips of average dimensions
2.4.times.2.7.times.1.9 mm were mixed and poured on a release paper
and heated in oven at 100 degrees for approximately 60 minutes.
After melting of polymer was observed, the wood-PCL mixture was
removed from oven and folded to shape of a thick plate (thickness
4-5 mm). After solidifying, the composite plate was placed back to
the oven and allowed to re-melt. The melting and shaping cycle was
repeated until a homogenous distribution of components was
achieved.
EXAMPLE 2
[0126] 85 g of .epsilon.-polycaprolactone CAPA 6800 and 4 g of
large aspen chips with average dimensions of
4.8.times.5.6.times.1.2 mm were melted to a wood-PCL composite
according to preparation method in Example 1. A light-weight
composite plate with optimum flexibility and rigidity for
orthopaedic casts was received.
EXAMPLE 3
[0127] 77 g of .epsilon.-polycaprolactone CARA 6800 and 33 g of
fine sawdust of mixed wood qualities (spruce, pine and birch) were
melted and mixed according to preparation method described in
Example 1 to achieve desired wood-PCL composite.
EXAMPLE 4
[0128] 700 g of .epsilon.-polycaprolactone CAPA 6800 and 300 g of
sprucedust with average dimensions of 2.times.2.times.0.2 mm and
were fed separately into a hopper of a Gimac mini twin-screw
extruder. Temperatures of screw, adapter and nozzle were close 130
deg C. The composite blend was pushed out through the compounder
nozzle (diameter 4 mm) and collected to the rolling belt. The
composite was cooled down by pressurized air while moving on the
belt. As a result a cylinder shaped homogenous mixture of wood
particles and polymer was received. Test samples for the mechanical
tests were prepared. according to method. described in Example
1.
[0129] The sizes of the wood particles used for the preparation of
the wood-PCL composites presented in Examples 1 to 4 are listed on
the following Table 1. The dimensions of wood particles presented
in Table 1 describe only average size wood material.
TABLE-US-00001 TABLE 1 dimensions of individual wood approximate
volume of particle (1 .times. w .times. t) individual wood
particles wood quality (mm) (mm.sup.3) spruce chips 2.4 .times. 2.7
.times. 1.9 ~10 aspen chips 4.8 .times. 5.6 .times. 1.2 ~30 sawdust
n.d. ~0.1 sprucedust 2 .times. 2 .times. 0.2 ~1
EXAMPLE 5
[0130] The influence of the reinforcing component on mechanical
properties was studied with the 3-point bending test, The flexural
strengths and modulus of the composites were measured with
universal testing machine Instron 4411. A pure PCL, without any
reinforcement was used as control.
[0131] The test samples (dimensions 55.times.10.5.times.5.5 mm)
were prepared by mixing constant ratio of different size wood chips
(30 weight %) and .epsilon.-polycaprolactone homopolymer (70 weight
%) and pressed into a Teflon mould. The melting and shaping of
samples until a homogenous distribution of components was achieved.
The samples were tested by constant cross head speed of 10 mm/min.
The 3-point bending forces arc presented graphically in FIG. 1 and
Young's modulus of elasticity in FIG. 2.
EXAMPLE 6
[0132] The densities of the samples prepared in Example 5 for
mechanical testing were measured by determining the dimensions of
the regular size samples and weighting them. The densities of the
composites are graphically presented in FIG. 3. As will appear,
composites according to the present invention have a considerably
smaller density than polycaprolactone as such.
EXAMPLE 7
[0133] The composite material prepared in the Example 3 was tooled
into a plate suitable for making a splint cast to support finger (a
"finger splint").
[0134] Approximately 5 grams of composite material was cast to a
plate at 100.degree. C. and allowed to cool down. The composite was
re-heated up to 70.degree. C. and when still warm and moldable
(above 65.degree. C.) the cast composite was manipulated with the
help of roller pin to form of a plate, thickness approximately 2
mm. The size of received composite plate was 35.times.60 mm.
[0135] FIG. 4 shows the use of the finger splint. The upper drawing
illustrates an injured (mallet) index finger 2 which has a rupture
of the extensor cordon. As will appear, the composite plate 1 can
be applied directly on the dorsal side of the mallet finger 2. The
composite plate can shaped to contour the finger so that the palmar
side of finger is left open. Upon cooling the composite splint
solidifies. Cooling was accelerated with a wet tissue. After
cooling, ordinary bandage (strips 3a and 3b) can be added to
immobilize the treated finger.
[0136] When removing the composite cast 1, a smooth surface inside
the splint is observed having no wrinkles or other irregular shapes
causing irritation of skin.
EXAMPLE 8
[0137] This example describes the production of a re-shapable wrist
cast 11 having the general shape shown in FIG. 5.
[0138] Approximately 100 grams of composite material prepared in
Example 1 was cast onto a metal plate and release paper at
100.degree. C. and allowed to cool down. The composite was
re-heated up to 70.degree. C.. and When still warm and moldable the
cast composite was manipulated to form of a thick plate, thickness
approximately 6 mm. Excess of materials was cut away with scissors
when still warm. The cut edges were gently contoured by hand in
order to soften the sharp edges. The size of received composite
plate was 12.times.25 cm.
[0139] The composite plate was applied directly on repositioned
wrist. The composite plate was left open on medial side of wrist.
The wrist was kept repositioned until the cast had solidified.
[0140] The semi-open wrist cast can be easily removed and re-shaped
if after imaging the clinician need to the repair the resulted
repositioning of wrist bones. The wrist cast may be re-softened at
the oven heated to 70.degree. C. or in water bath and replaced in
the corrected position on the wrist.
EXAMPLE 9
[0141] This example illustrates the preparation of an anatomic
ankle cast and the application thereof.
[0142] 200 grams of composite material manufactured in the Example
2 was cast on release paper at 100.degree. C. and allowed to cool
down. The composite was re-heated up to 70.degree. C. in heat oven
to resemble a thick plate, thickness approximately 8 mm. The
received composite plate, dimensions 15.times.40 cm was cut to
anatomical shape with scissors when it was still warm. Especially
area that is needed for the medical personnel to hold the leg when
repositioning the ankle was cut slightly open. Also, extra strips
were cut to be later attached on the anterior side of the cast. The
cut edges were gently contoured by hand in order to soften the
sharp edges.
[0143] FIG. 6 shows the general form of the produced cast plate.
Reference numeral 21 refers to the cast plate and numerals 22 to 24
to foldable flaps.
[0144] FIGS. 7a and 7b show how the composite plate 21 can be
reshaped when applied directly on the leg during repositioning of
the ankle after an injury.
[0145] Thus, in the application, the leg is kept repositioned until
the cast has solidified. When still warm, the cut flaps 22 and 23
are folded along folding lines 25 and 26 and compressed gently on
the anterior side of the composite cast. The cut flap 24 can in a
similar fashion be bent and shaped by folding its side portions
along folding lines 27 and 28. The material is non-tack but it
grips well with itself When it is still moldable, i.e. above
65.degree. C.
EXAMPLE 10
[0146] This example illustrates how a test according to the peel
adhesion test method shows the relative bond strength of a given
tape/bandage to surface (material and texture) of composite splint.
A molten WPC-material can be considered to be a pressure sensitive
adhesive. In this test gauze bandage is pressed with steel slab
surface of molten composite for 30 seconds and allowed to cool to
RT. After hardening of the composite gauze is peeled off at a
180.degree. angle from substrate at a constant peel rate by using
Instron mechanical testing device. The measurements were carried
out according to the modified standard SFS-EN 1939 (Standard Test
Method for Peel Adhesion of Pressure-Sensitive Tape).
[0147] A composite plate (widthlengththickness=60 mm.about.90
mm.about.3.5 mm) was placed into oven and allowed to set at a
temperature of 65.degree. C. during 30 minutes. After heating
procedure the composite plate was removed from the oven followed by
pressing a strip of elastic gauze bandage (width 50 mm, length
.about.250 mm, thickness 0.6 mm) to composite plate using a 3.3 kg
weight (0.09 bar). The gauze is folded twice on the composite plate
so that area size of wl=60 mm20 mm3.1 mm) is free. After 30 seconds
of pressing the slab is removed and the composite/gauze assembly
was allowed cool down to room temperature. After cooling the system
was placed into Instron testing machine. The loose end of the strip
was connected to the peel arm and the composite plate was mounted
horizontally onto a stage allowing .about.180.degree. angle to he
maintained as the tape was pulled from the surface of the composite
(FIG. 8). The rate of peeling was kept constant at 50 mm/min. The
peeling force as a function of distance was collected. The peeling
is ended before the last 20 mm of the test specimen is
achieved.
[0148] The composite manufactured of PCL-7 and small wood particles
in weight ratio of 60:40 (particle size between 0-0.8 mm) revealed
zero adhesive force. After changing the wood particles to larger
ones (particle size between 1 mm-5 mm) an adhesion force in the
range of 1 to 50 N was detected. This force is sufficient for
adhering the bandages to the surface to avoid sliding of them when
applying the splint on a patient. When the large wood particles
were combined with high molar mass polycaprolactone in weight ratio
of 70:30 adhesion force of 23 N was achieved.
[0149] It is worth mentioning that PCL-7 as such had an adhesive
force of 197 N. The adhesion is very strong and the gauge bandage
cannot be anymore removed by hands from the polymer sample.
EXAMPLE 11
[0150] Spruce chips were dried for 4 hours in 120.degree. C. and
polymer granules were used as received. Preliminary mixing of
virgin materials was carried out in a sealed plastic vessel. The
mixture (200 g wood chips/300 g PCL granules was poured to the feed
hopper connected to a Brabender single-screw extruder with four
heating zones. The rotational speed of the extruder was set to 50
rpm and the temperatures of all four zones were fixed at
130.degree. C. After compounding process with the extruder, the
formed composite material was heated in an oven to 125.degree. C.
to ensure its easy mouldability during the following calendering
process. The calendering of composite mixture to a homogeneous
plate was carried out in three phases which all included several
cycles, folding, cooling and reheating steps. The temperature of
calendar cylinder was fixed at 100.degree. C. After calendering
process the plate-like composite was cut with band-saw to size of
10 cm by 40 cm followed by one cycle calendering at 100.degree. C.
to achieve smooth surface to casting material.
* * * * *